Hybrid synchronous electric machine

ABSTRACT

A hybrid synchronous electric machine driven by the transverse magnetic flux has a rotor and a stator, the rotor armature has a massive cogged iron rings ( 12 ) in close vicinity of active parts of the motor, and cogged iron rings ( 14, 15 ) as component parts of the rotor are provided with cross-cut insulating gaps. Eddy current losses are low because eddy currents in cogged iron rings are impeded by cross-cut insulating gaps therein. Eddy currents in all passive parts of the motor (rotor armature ( 11 ), stator armature ( 1 ), ball bearing ( 9 ) and the like) are negligible since the current induced in the copper ring ( 12 ) neutralizes all the dissipated magnetic flux outside the active area of the motor. A hybrid synchronous electric machine which has low eddy current losses and high energy efficiency can be realized.

TECHNICAL FIELD

The present invention pertains to a synchronous hybrid electric machinewith transverse magnetic flux. In particular, the present relates to asynchronous hybrid electric machine whose structure is such that itminimizes eddy current losses in the motor and thus, it providesimproved energy efficiency as compared to conventional motors withsimilar construction.

PRIOR ART

Hybrid electric machines are a subclass of synchronous electricmachines. In construction they are similar to stepper motors within-built permanent magnets that increase magnetic filed density in theair gap, but unlikely the stepper motors, the hybrid electric machinesare usually fed by sinusoidal electric currents.

Special constructions of such motors are already known. Namely, hybridelectric machines with transverse magnetic flux have coils, which arecoaxial with the motor axis; their advantage is good energy efficiencydue to small ohmic losses in the coaxial coils.

A motor of this construction is described in the European patent0544200, wherein it has in each phase of the stator only one coil whichis coaxial with the motor axis and magnetises simultaneously a circulararray of stator yokes which encircle the stator coil. Similarly, in eachphase of the rotor this motor also has only one permanent magnet, whichis also coaxial with the motor axis and is placed between two iron ringswith salient poles on inner and outer circumference. The number ofsalient poles on each circumference equals the number of stator yokes.

The machine according to the above-described constructional solution hashigh torque per weight and good energy efficiency. This is advantageousespecially at low motor speed when efficiency of other electric motorsis usually low.

However, at high speed when magnetic fluxes in the motor alternate withconsiderably high frequency, we meet the problem of induced electriccurrents. The coin in each phase is coaxial with motor axis; thereforedissipated magnetic flux induces electric current in every such part ofthe motor which is also coaxial and electrically conducting. Such partsare especially the stator armature and the rotor armature (passive motorparts), and then also iron rings in the rotor.

Detailed analysis shows that in motors with transverse magnetic flux(that is, with coaxial coils) the currents induced in theabove-mentioned coaxial parts may be considerably great. They mayconsume much more energy than in corresponding parts of conventionalmotors with longitudinal magnetic flux. Energy losses of the describedtype are great especially when motor runs at high speed and torque(therefore, at high power); in this case they may be much greater thanall other losses taken together. Energy efficiency at high values ofmechanical power is then seriously spoiled and the motor may overhear.

One partial solution could be replacement of metal as the buildingmaterial in passive parts (especially in rotor and stator armature) withelectrically insulating materials (like ceramics or plastic materials),but usually such solutions are either too expensive (for ceramics) ormechanically inadequate (for plastics).

Consequently, there is a need in the art for additional high-powerhybrid electric machines, which have coaxial coils and transversemagnetic flux, yet their construction does not permit flow of inducedelectric currents in coaxial parts of the motor.

DISCLOSURE OF THE INVENTION

An object of the present invention is therefore to find such aconstructional solution of stator armature, rotor armature, and ironrings of the rotor, that induction of undesirable eddy currents withinthese parts is strongly damped or impeded.

The above object has been successfully achieved by a hybrid synchronousmachine with transverse magnetic flux comprising a rotor and a stator,the rotor armature comprising a rotor assembly having cogged iron rings,and the rotor assembly having cross-cut insulating gaps. The hybridsynchronous machine also has at least one massive copper ring in closevicinity of the active motor parts.

Namely, a hybrid synchronous electric machine with transverse magneticflux of the present invention is characterized in that it comprises: arotor and a stator; the rotor comprises at least one rotor assembly (13)of cogged iron rings (14, 15); and each assembly has at least onecross-cut insulating gap (22).

Further, the hybrid synchronous electric machine with transversemagnetic flux of the present invention is characterized in that itcomprises: a rotor, a stator, and a massive conducting ring (12); andthe conducting ring (12) is coaxial with the motor axis (5) and in closevicinity of the active area of the motor.

Here, the conducting ring (12) may be made of copper. The conductingring (12) may be part of the rotor armature (11).

It is desired that the cogged iron rings (14, 15) of the assembly (13)are electrically insulated from the supporting conducting ring (12).

The stator may be assembled by at least one circular array (2)constituted by U-shaped stator yokes (3 b or 3 c) spaced closelytogether, each yoke (3 b or 3 c) asymmetrically consisting of twoidentical, but mutually overturned iron parts (23 b, 24 b or 23 c, 24c).

The hybrid synchronous motor according the present invention has loweddy current losses because eddy currents in cogged iron rings areimpeded by cross-cut insulating gaps in these same iron rings, whileeddy currents in all passive parts of the motor (like rotor armature,stator armature, and ball bearings) are negligible since the currentinduced in the copper ring neutralizes all the dissipated magnetic fluxoutside the active area of the motor. Further, this motor is verycompact, strong and mechanically stable, despite low eddy currentlosses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an axonometric view of a two-phase synchronous hybrid electricmachine with transverse magnetic flux according to the invention, inpartial cross-section;

FIGS. 2(A) to 2(C) are axonometric views of an assemble of rotor ringsin one motor phase (examples A, B, C), showing a narrow insulating gapand insulating screws;

FIGS. 3(A) and 3(B) are an axonometric view of a circular array ofstator yokes (one phase, example A) of the motor according to theinvention, in partial cross-section, and a side view of the statoryokes, respectively;

FIGS. 4(A) and 4(B) are an axonometric view of a circular array ofstator yokes (one phase, example B) of the motor according to theinvention, in partial cross-section, and a side view of the stator yoke,respectively; and,

FIGS. 5(A) and 5(B) are an axonometric view of a circular array ofstator yokes (one phase, example C) of the motor according to theinvention, in partial cross-section, and a side view of the stator yoke,respectively.

SYMBOLS

-   1 Stator armature-   2 Circular array-   3, 3 b, 3 c Stator yokes-   4 Winding-   5 Motor axis-   6 Stator pole-   7 Stator pole-   9 Ball bearing-   11 Rotor armature-   12 Copper ring (conducting ring)-   13 Rotor assembly-   14, 15, 14 b, 15 b 14 c, 15 c Cogged rings-   16 to 19, 16 b to 19 b, 16 c to 19 c Rotor poles-   21 Screw-   22 Insulating gap-   23 b, 24 b, 23 c, 24 c Component parts of the stator yoke

BEST MODE FOR CARRYING OUT THE INVENTION

With respect to the drawings, examples of the present invention will nowbe explained.

In FIG. 1, a first embodiment (example A) of a two-phase synchronoushybrid electric machine with transverse magnetic flux according to theinvention is shown. To each side of the stator armature (1) is fixed acircular array (2) of U-shaped stator yokes (3) which encircle thestator winding (4) of the corresponding phase. The windings (4) arecoaxial with the motor axis (5).

Stator yokes (3) with salient poles (6, 7) are more precisely shown inFIG. 3. The yokes may be of bulk iron but it is better that the yokes(3) are lamination packages, as it is shown in FIGS. 1 and 3.

The rotor armature (11) connected to the stator armature (1) via ballbearings (9), is fitted with a massive copper ring (12) to which on eachside an assembly (13) of rotor rings is fixed. This assembly (13), whichis more precisely shown in FIG. 2(A) (example A), consists of two coggedrings (14, 15) of ferromagnetic material fitted with equally spacedrotor poles (16, 17, 18, 19) and a magnetized disk (20).

The ferromagnetic cogged rings (14, 15) can be lamination packages, justlike the stator yokes (3). (For the sake of clarity, these lamellae arenot shown in FIG. 2). The magnetized disk (20) is magnetized in theaxial direction so as to produce a magnetic flux that can be directedeither from the cogged ring (14) to the cogged ring (15) or in theopposite direction. The cogged rings (14, 15) and the magnetized disk(20) can be held together by means of screws (21), as shown moreprecisely in FIG. 2(A). The same screws (21) can be used to fasten therotor assembly (13) to the copper ring (12).

The cogged rings (14, 15) are electrically insulated from the supportingcopper ring (12), this can be achieved for instance by applying a thinceramic layer onto the stems of the screws (21) and onto the surface ofthe copper ring (12). The cogged rings (14, 15) have in at least oneplace a narrow insulating gap (22) to prevent free circulation ofcircular eddy currents, as is shown in FIG. 2(A). The same holds for themagnetized disk (20).

The cogged rotor rings (14, 15) and the stator yokes (3) are in themagnetic juncture; in each phase the number of stator yokes (3) is equalto the number of rotor poles (16, 17, 18, 19). The cogged rings (14, 15)in the assembly (13) of variant A are placed such that their outer poles(18, 19) are mutually shifted for one half of pole division, as shown inFIG. 2(A) (example A). The same holds for the inner poles (16, 17).

In example A there is also mutual shift for one half of pole divisionbetween the poles (16, 18) of the first cogged ring (14), and similarly,there is also mutual shift between the poles (17, 19) of the secondcogged ring (15). In FIG. 2(A) this relative position of opposing poleson inner and outer rotor circumference is more precisely shown by thedotted line S.

At a chose moment of observation, when the stator pole (6) covers therotor pole (17) and, due to the shift of the cogged ring (14) againstthe cogged ring (15), the stator pole (7) covers the rotor pole (18), acurrent starts running in the winding (4) in such a direction that thedensity of magnetic field in the air gap between the stator pole (6) andthe rotor pole (17) of the cogged ring (15), and between the stator pole(7) and the rotor pole (18) of the cogged ring (14) decreases, while thedensity of magnetic field in the air gaps between the stator pole (6)and the rotor pole (16) of the cogged ring (14) and between the statorpole (7) and the rotor pole (19) of the cogged ring (15) increases.

Because of such momentous magnetic state the stator poles attract therotor poles towards a position which is shifted by ½ of the pole'sdivision with regard to the position at the chosen moment, so that inthe end position of observation the stator pole (6) coincides with therotor pole (16) of the cogged ring (14), and the stator pole (7)coincides with the rotor pole (19) of the cogged ring (15). At thismoment the direction of current in the winding (4) inverts. This causesthe rotor to move forwards, so that it reassumes the initially observedposition of mutual covering of the rotor and stator poles. Through thechange of current direction in the stator winding (4) the rotation ofrotor is enabled, while the change itself can be achieved by electroniccommutation.

In motors with transverse magnetic flux considerable voltages areinduced in all active parts which are coaxial with the motor axis (5).In the motor according to the invention, such parts are the cogged rings(14, 15) and the magnetized disk (20). These ring-like parts (14, 15,20) are cut by insulating gap (22) in at least one place so that theinduced voltage cannot drive circular currents around these rings (14,15, 20). This is shown in FIG. 2(A) (example A). The gap (22) can befilled with some electrically insulating adhesive material. The inducedcurrents also cannot bypass the insulating gap via the copper ring (12)since the rings (14, 15, 20) are electrically insulated from thesupporting copper ring (12).

In this way eddy current losses in the active parts of the motor areconsiderably reduced, which is significant especially at high motorspeed and at high torque when the magnetic flux changes are great. Itcan be shown that the insulating gap (22) in each rotor assembly (13)can reduce eddy current losses in the cogged iron rings by a factor ofapproximately 10.

There are also eddy current losses in the passive parts of the motor,namely in the rotor armature (11), stator armature (1), and ballbearings (9). Unluckily, they cannot be reduced in the same way sincethese parts are the supporting parts of the motor. Namely, insulatinggaps in the supporting parts would reduce the mechanical precision andwould spoil compactness of the motor. According to the invention, thisproblem is solved by a massive copper ring (12) which is placed outsidethe active area with a strong magnetic field, but still is in closevicinity of this active area. So this ring (12) does not affect themagnetic field in the active parts, yet it considerably affects thedissipated magnetic fields outside of the active area.

This dissipated magnetic flux of the machine with transverse magneticflux induces circular AC electric current around the copper ring (12).This induced AC current produces its own magnetic flux, which is coupledto the original dissipated magnetic flux. A detailed analysis (accordingto conventional methods in theory and practice of electric machines)shows that the original dissipated AC magnetic flux and the induced ACmagnetic flux approximately cancel each other if the quantity Q definedby relation:Q=ξ/(μ_(o)·

·ω)  (1)is much less than 1.In the above formula the following notations are used:ξ is the specific electric resistance of the material used in the ring(12). For copper at working temperature of the motor,ξ is approximately 2·10⁻⁸Ωm.μ_(o) is the induction constant (4π·10⁻⁷ Vs/Am)S is the cross-section area of the ring (12) in units of m².In FIG. 1 this is marked by the shaded cross-section of the ring (12).ω is the circular frequency of the electric current in the motor coils(in units of s⁻¹) Usually we take ω at nominal speed of the motor.

is a dimensionless parameter depending on the geometry and preciseproportions of the motor. The parameter

is usually between 0.5 and 0.7 for constructional designs where theconducting ring (12) is exactly between the active areas of the twophases of the motor with transverse magnetic flux. This is the caseshown in FIG. 1 where we see the conducting ring (12) between two coggedrings (14) of the two phases of the motor according to the invention. Ifthe conducting ring (12) is not in this central position, then theparameter

is smaller. The construction with greater

is advantageous (see the text below).

The solution according to the present invention applies inmost of thecases, except in such cases when the nominal motor speed is so low thatwe cannot get Q smaller than unity. In these exceptional cases thecopper ring (12) is not used, and the rotor armature (11) can extendinto the area near the active parts of the motor. Then it is good thatthe armatures (11) and (1) are then made of materials with much higherelectric resistance ξ, since in such cases we have no other means toreduce eddy currents in the passive parts of the motor.

Luckily, it turns out that for most practical application, the quantityQ is indeed quite smaller than 1. In every such case the dissipatedmagnetic flux is nearly completely cancelled out. Then the eddy currentlosses in the motor housing (stator armature) and in the rotor armatureare very small. What remains are practically only the losses in thecopper ring (12), but also these losses are much smaller than ohmiclosses in the motor coils (the ratio between these two types of lossesis just of the order of Q). Hence, if Q is much smaller than 1, thenlosses in the copper ring are negligible if compared to the ohmic lossesin the coils (4). Further, eddy current losses in rotor and statorarmature (11, 1) are in the case of small Q even much smaller thanlosses in the copper ring (12). Hence, overall eddy current losses aremuch smaller than eddy current losses in motors without the conductingring (12) where losses in the armature would be quite large.

It is evident that one should look for such a constructional solution ofthe machine with transverse magnetic flux that the parameter Q is muchsmaller than 1. This can be achieved by a conducting ring (12) withgreat cross-section S and small specific electric resistance ξ.Therefore the proposed choice is use of a massive copper ring (12). Theholes for screws (21) should not be too wide so that the passage ofelectric current along the conducting ring (12) is not considerablyimpeded by them.

The ring (12) forms an attached part of the rotor armature (11), soinstead of pure copper (oxygen free & high conductivity copper) which istoo soft for mechanical applications, one can make a compromise by useof copper with small addition of alloying metals. In this way one canquite easily and sufficiently increase the mechanical stiffness withoutexcessively increasing the specific resistance ξ.

Therefore, the problem of eddy current losses has been successfullysolved by a hybrid synchronous machine with transverse magnetic flux,the rotor armature (11) comprising of at least one massive copper ring(12) in close vicinity of the active motor parts, and the rotor rings(14, 15, 20) having at least one cross-cut insulating gap (22).

The described solution also improves the compactness of motor. Namely,the cogged iron rings (14, 15) with cross-cut insulating gaps (22) aremore flexible than rings without these gaps (22), especially in the casethey are lamination packages. Hence, the rotor rings (14, 15, 20) need afirm support, which can be easily provided by the massive copper ring(12).

Another improvement in motor compactness, which is also a matter of thepresent invention, is shown in FIGS. 4 and 5. Constructions with theseimprovements are described as examples B and C, which introduce somemodifications to the original example A shown in FIG. 3. As we see inFIG. 1 and in FIG. 3, in example A the U-shaped stator yokes (3) in thecircular array (2) are separated from each other. Some additional part(e.g., made from plastic material) must provide for the desiredseparation between the yokes (3) in example A.

As we see in FIG. 4, in example B this plastic part is no morenecessary, since the stator yokes (3 b) are not separated amongthemselves. Instead of one simple and symmetrical yoke (3) in variant A,in variant B we have a yoke (3 b) of more complicated shape. In fact,this yoke (3 b) is a pair of two parts (23 b, 24 b). These two parts (23b, 24 b) are equal, but the first part (23 b) is turned upside down,while the second part (24 b) is turned downside up, as is seen in FIG.4.

In example B one yoke (3 b) is carrying the same magnetic flux as oneyoke (3) in the example A. But since there is no distance between theyokes (3 b), each yoke (3 b) is twice wider than the yoke (3) of variantA, and consequently the radial thickness of the yoke (3 b) can be onlyone half of the corresponding thickness in variant A. This can be seenif we compare FIGS. 3 and 4. So also the housing of the motor can besmaller, which, together with dense packing of the stator yokes (3 b),contributes to motor compactness. Another advantage is easier assemblingof the motor, since in variant B there is no need to provide forseparation between the stator yokes (3 b).

Very similar argumentation holds also for example C (shown in FIGS. 2(C)and 5), wherein stator yokes (3 c) are also assembled closely togetherinto a circular array (2). Each yoke (3 c) is in fact a pair of twoparts (23 c, 24 c) which are again equal, with provision that the firstpart (23 c) is turned upside down and the second part (24 c) is turneddownside up. Also the yokes (3 c) make motor similarly compact and easyto assemble.

Due to different angular poison of stator poles (6, 7) in examples B andC, in examples B and C the relative poison of rotor poles slightlydiffers from the one described for example A. Corresponding rotor partsare shown in FIGS. 2(B) and 2(C).

In example B of FIG. 2(B), the cogged rings (14 b, 15 b) in the assembly(13) are placed such that their outer poles (18 b, 19 b) are notmutually shifted. The same holds for mutual shift of the inner poles (16b, 17 b). There is also no mutual shift between the poles (16 b, 18 b)of the first cogged ring (14 b), and similarly, there is also no mutualshift between the poles (17 b, 19 b) of the second cogged ring (15 b).In FIG. 2 (variant B) this relative position of opposing poles on innerand outer rotor circumference is more precisely shown by the dotted lines.

In example C, the cogged rings (14 c, 15 c) in the assembly (13) areplaced such that their outer poles (18 c, 19 c) are mutually shifted forone half of pole division (like in example A), and the same holds formutual shift of the inner poles (16 c, 17 c). But there is no mutualshift between the poles (16 c, 18 c) of the first cogged ring (14 c),and similarly, there is also no mutual shift between the poles (17 c, 19c) of the second cogged ring (15 c). Again, in FIG. 2(C) (example C)this relative poison of opposing poles on inner and outer rotorcircumference is more precisely shown by the dotted line s.

In this way the same magnetic juncture of rotor and stator poles can beachieved in all three examples (A, B and C), which leads also toequivalent functioning in all three cases.

INDUSTRIAL APPLICABILITY

As explained above, the hybrid synchronous electric machine driven bythe transverse magnetic flux of the present invention is constituted tohave the rotor and the stator, and the rotor armature has the coggediron rings provided with at least one cross-cut insulating gap. Further,according to the present invention, the machine has the rotor, thestator and the conducting ring; the conducting ring is arranged coaxialwith the motor axis and is in the close vicinity of the active area ofthe motor.

According to the present invention, the hybrid synchronous motor havinglow eddy current losses can be obtained, because eddy currents in coggediron rings are impeded by cross-cut insulating gaps in these same ironrings. In addition, eddy currents in all passive parts of the motor(like rotor armature, stator armature, and ball bearings) are negligiblesince the current induced in the copper ring neutralizes all thedissipated magnetic flux outside the active area of the motor.

Further, according to the present invention, the hybrid synchronousmotor can be realized which is very compact, strong and mechanicallystable, despite low eddy current losses.

1. A hybrid synchronous electric machine comprising: a rotor and astator; the rotor comprising at least one assembly of cogged iron rings,and each assembly having at least one cross-cut insulating gap; theconducting ring being coaxial with a motor axis and in close vicinity ofan active area of the motor; wherein the conducting ring is formed aspart of a rotor armature.
 2. The hybrid synchronous electric machineaccording to claim 1, wherein the conducting ring is made of copper. 3.A hybrid synchronous electric machine comprising: a rotor and a stator;the rotor comprising at least one assembly of cogged iron rings, andeach assembly having at least one cross-cut insulating gap; theconducting ring being coaxial with a motor axis and in close vicinity ofan active area of the motor; wherein the cogged iron rings of the rotorassembly are supported by the conducting ring and are electricallyinsulated from the conducting ring.
 4. A hybrid synchronous electricmachine comprising: a rotor and a stator; the rotor comprising at leastone assembly of cogged iron rings, and each assembly having at least onecross-cut insulating gap; wherein the stator comprises at least onecircular array, and the circular array is constituted by U-shaped statoryokes spaced with one another.
 5. A hybrid synchronous electric machinecomprising: a rotor and a stator; the rotor comprising at least oneassembly of cogged iron rings, and each assembly having at least onecross-cut insulating gap; wherein the stator comprises at least onecircular array, the circular array comprises stator yokes closelyarranged with each other, and each stator yoke asymmetrically consistsof two identical, but mutually overturned iron parts.
 6. A hybridsynchronous electric motor comprising: a rotor, a stator and aconducting ring; the conducting ring being coaxial with a motor axis andin close vicinity of an active area of the motor; wherein the conductingring is formed as part of a rotor armature.
 7. The hybrid synchronouselectric motor according to claim 6, wherein the conducting ring is madeof copper.
 8. A hybrid synchronous electric motor comprising: a rotor, astator and a conducting ring; the conducting ring being coaxial with amotor axis and in close vicinity of an active area of the motor; whereinthe stator comprises at least one circular array, and the circular arrayis constituted by U-shaped stator yokes spaced with one another.
 9. Ahybrid synchronous electric motor comprising: a rotor, a stator and aconducting ring; the conducting ring being coaxial with a motor axis andin close vicinity of an active area of the motor; wherein the statorcomprises at least one circular array, the circular array comprisesstator yokes closely arranged with each other, and each stator yokeasymmetrically consists of two identical, but mutually overturned ironparts.